Condensed Consolidated Balance Sheets (Unaudited) (Parenthetical) (USD $)	Mar. 31, 2013	Dec. 31, 2012
Stockholders' equity
Preferred stock, par value	$ 0.001	$ 0.001
Preferred stock, shares authorized (actual number)	25,000,000	25,000,000
Preferred stock, shares issued (actual number)	0	0
Preferred stock, shares outstanding (actual number)	0	0
Common stock, par value	$ 0.001	$ 0.001
Common stock, shares authorized (actual number)	600,000,000	600,000,000
Common stock, shares issued (actual number)	408,246,533	406,163,194
Treasury stock, shares (actual number)	34,715,913	30,601,262